This award will provide salary support that will significantly reduce the teaching load of the candidate and therefore will allow much more effort to be devoted to research on solution structural studies of RNAs. Specifically, the award will cut the teaching load of the candidate in half from the normal two (3 credit) courses per year to a single course. This reduced teaching load means that the candidate can take full advantage of unique research opportunities that the University of Colorado at Boulder offers for studies of RNA structure. Boulder has eight research groups that are extremely active in the areas of RNA biochemistry and molecular biology. The candidate moved to Boulder in 1988 to take advantage of this environment and since that time has set up a research effort in nuclear magnetic resonance (NMR) structural studies of RNA. This work complements the previous research by the candidate in the areas of NMR studies of DNA and antimicrobial peptides. The increased time that be devoted to research by this reduction of teaching load will allow the next phase of the NMR structural studies of RNA to proceed at an accelerated pace. This phase will involve application of heteronuclear multi-dimensional NMR experiments to the structure determination of biologically active RNAs. The heteronuclear NMR experiments are presently revolutionizing solution structure determinations of proteins, but these techniques have yet to be applied to studies of RNAs. The RNAs that will be studied include: i) two RNA enzymes, the self-cleaving hammerhead and hairpin RNA domains, both of which have potentially important in vivo applications as site-specific RNA endonucleases which can be designed to specifically cleave a target mRNA or the genome of an RNA virus such as HIV; ii) a yeast tRNA(Phe) system that will serve as a model system for developing techniques for identification of tertiary interactions in RNAs; and iii) several RNA structural motifs including a set of unusually stable and naturally occurring RNA hairpins that contain tetranucleotide loops. The structural information provided by the NMR experiments will be combined with additional biological and biochemical data in order to improve structure-activity relationships for RNAs.